1. Field of the Invention
The invention relates generally to three-phase induction motors and particularly to a device for controlling the speed of an induction motor without the use of brushes.
2. Description of the Prior Art
In the art of varying speeds in electric motors and, through them, in electric machinery various alternatives are under development, one of the most usual being the direct current motor, the motor using eddy currents, the one using parasite currents, the one with slip-rings and others not as common, such as the variable frequency motor, which is highly complicated, and also the Schrague motor: not to mention the various mechanical systems such as pulleys and conical rotors, and some electromagnetic types with variable coils within the motor which change from delta to star, or even with very special coils in its primary and secondary stages, in order to provide induced voltage, control voltage, drive voltage, regulatable exciter voltages and line voltages.
Generally speaking, the hoped-for results have been obtained insofar as variable speed is concerned, but the specialization of these motors has been maintained, making them expensive and difficult to produce.
Industry has been deprived of the application of variable-speed on a large scale by the costs, and also by the difficulty of maintenance and the repair of motors, even ordinary ones such as those with direct current which--cause problems through their brushes and collectors.
Electric motors without brushes, if they are controlled by frequencies in order to make them variable-speed, do not present the same problems of brushes, collectors, etc. but on the other hand the electronic control is so complicated and costly that even the manufacturers are careful not to recommend it.
A variable speed, electric induction motor includes a triphasic stator, a rotor shaft having a rotor mounted thereon, the rotor having longitudinal grooves on an outer face thereof carrying three induction coils. The improvement includes a light-dependent resistance mounted on an end of the rotor shaft, four controlled diodes mounted in two pairs on the rotor, each diode having a control electrode and each pair of the diodes connected to one of the induction coils. The light dependent resistance is electrically connected to the control electrodes such that the current flowing to the control electrodes is dependent on the light incident on the light-dependent resistance.
The object of the present invention is to provide variable-speed-electric induction motors without brushes.
It is also the object of the present invention that the motor should use alternating current and should feed directly off the fixed frequency circuit, even though it is of variable speed.